Light is the source of energy that fuels plant growth through photosynthesis. Light is also a developmental signal that modulates morphogenesis, such as de-etiolation and the transition to reproductive development. Since plants cannot choose their surroundings, they are forced to adapt their growth to ambient light conditions and have evolved complex mechanisms for monitoring the quantity and quality of the surrounding light. For example, many kinds of plants respond to growth under dense canopies or at high densities by growing faster and taller (Cerdan and Chory (2003) Nature, 423:881). Densely planted crops tend to place energy into stem and petiole elongation to lift the leaves into the sunlight rather than putting energy into storage or reproductive structures. The response to low light conditions negatively affects crop yields by reducing the amount of harvestable products such as seeds, fruits and tubers. In addition, tall spindly plants tend to be less wind resistant and lodge more easily, further reducing crop yield.
There is a continuing need for plants that can thrive under less than optimal environmental conditions. One strategy to improve a plant's ability to withstand suboptimal environmental conditions relies upon traditional plant breeding methods. Another approach involves genetic manipulation of plant characteristics through the introduction of exogenous nucleic acids conferring a desirable trait.